This invention relates generally to the control of electroluminescent loads. More particularly, this invention relates to a resonant switch phase control for dimming control of electroluminescent loads.
Electroluminescent loads such as electroluminescent lamps in the shape of a panel can be used to provide a source of illumination in many instances. Such electroluminescent (EL) lamps or panels generally consist of transparent conductive electrodes separated by a dielectric containing a luminescent phosphor. The amount of illumination provided by a panel or lamp is determined by the voltage across the layer and the frequency applied to it.
One application of electroluminescent panels is in the aircraft field wherein such panels are used to illuminate the entrance for the prod used in mid air aircraft refueling and also to provide illumination of the aircraft during formation flying for visual sighting by other pilots in the formation.
In this application, it is necessary that the EL panels can be dimmed reliably to suit the particular conditions and to minimize the possibility of a rise in illumination when not desired. Such EL panels are connected to a power source within the aircraft which is generally 115 volts, 400 Hz power. Proper control of the voltage to the EL panel is necessary to ensure that the proper level of illumination is obtained at a particular time. During certain conditions, such as night formation flying where there may be the presence of hostile forces, maximum illumination is not desirable. Accordingly, such a circuit should be provided with a dimming control.
Additionally, the input voltage from the aircraft may vary so that without proper control, the voltage to the EL lamp may drop, resulting in a loss of illumination or, if the particular desired illumination is relatively low, requiring a low voltage input, the illumination from the EL lamp may increase at an inappropriate time due to an unexpected increase in the input voltage.